Shell proteins and microstructural analysis identify the origin of shell arts with species resolution in pearl oysters

Molluscan shells are diverse, beautiful, and mechanically robust. They were commonly used by humans during ancient times as money, decorative objects, or functional tools. Luodian, a unique shell art in China dating back 3000 years, has served as a cultural carrier between China and Europe. To understand the production processes as well as underlying cultural contexts, it is important to identify the material origin of the art. This study combined proteomics and microstructural analysis to identify the raw material origins of three Luodian samples from the Qing Dynasty with species resolution and potential maturity levels. Shell proteomics and multiple sequence alignment have identified key shell matrix proteins (N66 and Pif) from Pinctada maxima, a pearl oyster distributed in the Indo-Pacific region. Although other factors (temperature, salinity, etc.) may contribute to the thickness of nacreous tablets in the shell, the thickness is inversely proportional to the shell size in the pearl oyster. We inferred the maturity of raw materials in different Luodian samples, which are tailored to different purposes. This study provides a framework and foundation for identifying the origin of various shell arts, especially those made from pearl oysters.